Phase discriminator



Aug. 14, 1956 l. H. SWIFT 2,759,109 PHASE DISCRIMINATOR Filed May 28, 1954 B +8 1 |4 INPUT B I 60 50 INVENTOR. IRVIN H. SWIFT ATTORNEYS United States Patent PHASE DISCRIMINATOR Irvin H. Swift, China Lake, Califi, assignor to the United States of America as represented by the Secretary of the Navy Application May 28, 1954, Serial No. 433,318

Claims. (Cl. 3772) (Granted under Title 35, U. S. Code (1952), see. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to phase discriminators, and in particular to an improved phase discriminator which produces a D. C. output voltage, the magnitude of which is directly proportional to the amount of departure from quadrature of two input voltages and the polarity of which depends on the direction of the departure.

The phase discriminator constituting this invention is an improvement over the phase discriminator disclosed in U. S. patent application No. 290,609, filed May 28, 1952, entitled System for Analogue Computing by John E. Richardson.

It is, therefore, an object of this invention to provide an improved phase discriminator which produces a D. C. output voltage, the polarity of which is a function of the direction of departure of two input signals from quadrature and the magnitude of which is a function of the amount of the departure.

It is a further object of this invention to provide an improved phase discriminator which has a relatively low output impedance.

It is a still further object of this invention to provide an improved phase discriminator in which the number of components is minimized.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same become better understood by reference to the following detailed description when considered in connection with the accompanying drawing wherein:

Fig. 1 is a schematic diagram of the phase discriminator, and

Figs. 2, 3 and 4 are vector diagrams to facilitate explaining the operation of the discriminator.

Referring now to Fig. 1, input A. C. voltage A is applied across primary coil of transformer 12, and A. C. input voltage B is applied across primary coil 14 of trans former 16. Secondary coil 18 of transformer 12 is provided with a center tap 20. Transformer 16 has two secondary coils 22, 24 of an equal number of turns, and each of the secondary coils of transformer 16 is provided with center taps 26, 28, respectively. Center tap 26 of secondary coil 22 of transformer 16 is connected to terminal 30 of secondary coil 18 of transformer 12. Center tap 28 of secondary coil 24 of transformer 16 is connected to terminal 32 of secondary coil 18 of transformer 12. Terminal 34 of coil 22 is connected to the center tap of coil 18 through current rectifier 36 and resistor 38. Terminal 40 of coil 24 is connected to center tap 20 of coil 18 through rectifier 42 and resistor 38. Terminal 44 of coil 22 is connected to center tap 20 through rectifier 46 and resistor 48, and terminal 50 of secondary coil 24 is connected to center tap 20 through rectifier 52 and resistor 48.

Output terminal 54 of the phase discriminator is connected to terminal 56 of resistor 38 and output terminal 58 of the phase discriminator is connected to terminal 60 of resistor 48. The resistance of resistor 38 substantially equals the resistance of resistor 48. Current rectifier 36 is connected to permit conventional current to flow from terminal 34 of coil 22 to terminal 56 of resistor 38, rectifier 42 is connected to permit current to flow from terminal 40 of coil 24 to terminal 56, current rectifier 46 is connected to permit current to flow from terminal 44 of coil 22 to terminal 60 of resistor 48, and current rectifier 52 is connected to permit current to flow from terminal 50 of coil 24 to terminal 60. Rectifiers 36, 42, 46, 52 may be of any suitable type, such as selenium, copper oxide, germanium, silicon, etc.

The sinusoidal voltage between center tap 20 and terminal 30 of coil 18 can be represented by the vector +2: and the voltage between center tap 20 and terminal 32 by the vector -71 Similarly, the voltages between terminals 34 and 44 with respect to center tap 26 of coil 22 can be represented by vectors +l and respectively, and the voltages between terminals 40 and 50 with respect to center tap 28 of coil 24 can be represented by vectors and +T3 Then, the voltage across resistor 38 will equal the magnitude of the vector sum of K and 13 {IA-F], or [Z+|. The voltage across resistor 38 will always be positive with respect to center tap 20 because of the manner in which current rectifiers 36, 42 are connected in the circuit. The voltage across resistor 48 will equal the magnitude of the vector difference of K and [Z l,

or [Z+F|. The voltage across resistor 48 will also always be positive with respect to the center tap 20. The D. C. potentials across resistors 38, 48 will be pulsating, the wave forms of which will be similar to that of full wave rectified sinusoidal A. C. voltages.

When voltages represented by A and B are in phase quadrature, as illustrated in Fig. 2, it can be seen that the magnitudes of the vector sum of X and 5 equals the magnitude of the vector difference. The D. C. components of the voltages across resistors 38, 48 will be equal, and no D. C. potential will exist between output terminals 54, 58. W

If the phase angle between K and B is less than or acute, as shown in Fig. 3, the magnitude of the vector sum of A and I? will be greater than the magnitude of the vector difference. The D. C. voltage across resistor 38 will be greater than the D. C. voltage across resistor 48, so that output terminal 54 will be at a higher D. C. potential than output terminal 58.

If the phase angle between Kand E is greater than 90, or obtuse, as illustrated in Fig. 4, the magnitude of the vector sum of X and ii is less than the magnitude of the vector difference. The D. C. voltage across resistor 48 will then be greater than the D. C. voltage across resistor 38, so that the D. C. potential of terminal 58 will be greater than the D. C. potential of terminal 54.

In the discriminator constituting this invention it is not essential that one of the input voltages be of greater magnitude than the other.

If D. C. current is to be drawn from the output terminals 54, 58, a choke of 10 henries, or greater, in series with the load is necessary if the input impedance is to remain linear. Since the discriminator may be used to supply current to the control windings of a magnetic amplifier which has the necessary high inductance, no choke is illustrated in Fig. 1.

In the discriminator comprising this invention, the output impedance is double the forward resistance of a single current rectifier, and four current rectifiers are required.

In the discriminator disclosed in U. S. patent application No. 290,609, identified above, the output impedance is four times the forward resistance of a single current rectifier, and eight current rectifiers are required.

While the discriminator constituting this invention has been described and its operation explained on the basis that the input voltages are normally in phase quadrature, the circuit may also be used as a phase sensitive detector which produces a D. C. output voltage whose maximum value is twice the amplitude of the smaller input signal when the input signals are in phase or 180 out of phase, and whose polarity indicates the relative phase of the two input signals; i. e., the output voltage is positive when the phase angle between the input voltage is less than i90 and negative when the phase angle is greater than :90".

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A discriminator comprising a first transformer having a primary coil and a secondary coil, the secondary coil having a center tap, a second transformer having a primary coil and two secondary coils, said secondary coils being center tapped and having substantially the same number of turns, and circuit means including resistors and current rectifiers interconnecting the secondary coils of said transformers for producing across one resistor a first D. C. potential equal to the magnitude of the vector sum of the voltages induced in the secondary coils of said transformers and for producing across a second resistor a second D. C. potential of the same polarity as l the first D. C. potential and equal to the magnitude of the vector difference of the voltages induced in the secondaries of said transformers when a first input voltage is applied across the primary coil of the first transformer and a second input voltage is applied across the primary coil of the second transformer.

2. A discriminator comprising a first transformer .having a primary coil and a secondary coil, the secondary coil having a center tap, a second transformer having a primary coil and two secondary coils, said secondary coils being center tapped and same number of turns, and circuit means including resistors and current rectifiers interconnecting the secondary coils of said transformers for producing across one resistor a first positive D. C. potential equal to the magnitude of the vector sum of the voltages induced between the ends and center taps of the secondary coils of said transformers and for producing across a second reslstor a second positive D. C. potential equal to the magnitude of the vector difference of the voltages induced between the ends and center taps of 'the secondaries of said transformers when a first input voltage is applied across the primary coil of the first transformer and -a second input voltage is applied across the primary coil of the second transformer.

3. A discriminator comprising a first transformer having a primary coil and a secondary coil, the secondary coil having a center tap, a second transformer havmga primary coil and first and second secondary coils, said first and second secondary coils having the same number of turns and each having a center tap, first circuit means connecting one end of the secondary coil of the first transformer with the center tap of the first secondary coil of said second transformer, second circuit means connected having substantially the to the other end of the secondary coil of the first transformer with the center tap of the second secondary coil of said second transformer, third circuit means including a resistor and current rectifying means connected between the center tap of the secondary coil of the first transformer, one end of the first secondary coil of the second transformer, and one end of the second secondary coil of the second transformer, and fourth circuit means including a resistor and current rectifying means connected between the center tap of the secondary coil of the first transformer, the other end of the first secondary coil of the second transformer, and the other end of the second secondary coil of the second transformer, said third circuit means being so arranged and connected that a D. C. potential is developed across the resistor of said third circuit means which is a function of the magnitude of the vector sum of a first A. C. voltage applied across the primary coil of the first transformer and of a second A. C. voltage applied across the primary coil of the second transformer, and said fourth circuit means being so arranged and connected that a D. C. potential is developed across the resistor of said fourth circuit means which is substantially a function of the magnitude of the vector difference of said first and second voltages.

4. A discriminator as defined in claim 3 in which the resistance of the resistor of said third circuit means substantially equals the resistance of the resistor of said fourth circuit means.

5. A discriminator comprising a first transformer having a primary coil and a secondary coil having a center tap, a second transformer having a primary coil and two secondary coils having center taps and the same number of turns, first circuit means connecting an end of the secondary coil of the first transformer with the center tap of one of the secondary coils of the second transformer, second circuit means connecting the other end of the secondary coil of the first transformer with the center tap of the other secondary coil of the second transformer, current rectifying means connected to the ends of the secondary coils of the second transformer to permit current to fiow from the ends of said coils, "a first resistor having one terminal connected to the center tap of the secondary coil of the first transformer and the other terminal connected to the current rectifying means at one end of one of the secondary coils of the second transformer and said other terminal also connected to the current rectifying means at the opposite end of the other of said secondary coils of the second transformer, a sec ond resistor equal to the first resistor and having :one terminal connected to the center tap 0f the secondary coil of the first transformer and the other terminal connected to the current rectifying means at the other ends of the secondary coils of the second transformer, whereby, when a first A. C. input voltage is applied across the primary coil of the first transformer and a second A. C. input voltage is applied across the primary coil of the second transformer, D. C. potentials are developed across the first and second resistors, the difference between said D. C. potential being a function of the direction of .departure and of the magnitude of departure of said first and second A. C. input voltage from phase quadramre.

References Cited in the file of this patent UNITED STATES PATENTS 

